1. Field
This document relates to a liquid crystal display capable of improving the distortion of the picture quality according to external light.
2. Related Art
A liquid crystal display displays an image by controlling the light transmittance of a liquid crystal layer in response to a video signal through an electric field which is applied to the liquid crystal layer. The liquid crystal display is a kind of flat display device having the advantages of a small size, slimness, and low power consumption and is being used for portable computers (e.g., notebook PC), office automation devices, and audio/video devices. In particular, an active matrix-type liquid crystal display in which switching elements are formed in respective liquid crystal cells is advantageous in that it can implement motion images because the switching elements can be actively controlled.
A thin film transistor (hereinafter referred to as a ‘TFT’) as in FIG. 1 is for the most part used as the switching element of the active matrix-type liquid crystal display.
Referring to FIG. 1, the active matrix-type liquid crystal display is configured to convert digital video data into an analog data voltage on the basis of a gamma reference voltage and to supply the converted analog data voltage to a data line DL and a scan pulse to a gate line GL at the same time, thereby charging a liquid crystal cell Clc with the data voltage. To this end, the gate electrode of a TFT is connected to the gate line GL, the source electrode of the TFT is connected to the data line DL, and the drain electrode of the TFT is connected to the pixel electrode of the liquid crystal cell Clc and one of electrodes of a storage capacitor Cst. A common voltage Vcom is supplied to the common electrode of the liquid crystal cell Clc. When the TFT is turned on, the storage capacitor Cst functions to charge a data voltage supplied from the data line DL and to constantly maintain the voltage of the liquid crystal cell Clc. When a scan pulse is supplied to the gate line GL, the TFT is turned on to form a channel between the source electrode and the drain electrode, and so voltage on the data line DL is supplied to the pixel electrode of the liquid crystal cell Clc. At this time, the arrangement of liquid crystal molecules of the liquid crystal cell Clc is changed by an electric field between the pixel electrode and the common electrode, thereby modulating incident light.
A picture quality which is felt by a viewer through this liquid crystal display may be easily distorted according to external environments (the illuminance of external light, the color temperature of external light, etc.). This is because a human's eyes differently feel the color temperature of reference white according to the color temperature (or illuminance) of external light. For example, in a red lighting living room as in FIG. 2, a viewer can recognize white color having slightly red color as ‘colorless white color.’ Accordingly, a sensitivity for the red color is relatively low, but a sensitivity for blue color (i.e., color corresponding to the red color) is relatively high. On the other hand, in a blue lighting living room as in FIG. 2, a viewer can recognize white color having slightly blue color as ‘colorless white color.’ Accordingly, a sensitivity for the blue color is relatively low, but a sensitivity for red color (i.e., color corresponding to the blue color) is relatively high.
Such distortion of the picture quality results from the fact that an R gamma curve, a G gamma curve, and a B gamma curve are fixed according to a preset specification (1.8 gamma to 2.2 gamma) irrespective of corresponding viewing environments and maintain a constant color temperature. Consequently, color which is felt through a conventional liquid crystal display is distorted from the original color according to a change in the color temperature (or illuminance) of external light.